Objective: To examine (1) the concordance of manual and automated para-symphyseal angle of progression (psAOP) measurements, (2) the repeatability of psAOP, head-symphysis distance, head-perineum distance, and sonographic cervical dilatation, and (3) the value of transperineal ultrasound (TPU) in predicting induction of labor (IOL) outcome. Methods: We performed a prospective study in 308 women with singleton pregnancies undergoing IOL at term. Logistic regression analysis was used to determine which maternal factors, Bishop score, method of IOL, and TPU parameters were significant predictors of cesarean section (CS) and CS due to no progress (CS-NP). Results: There was vaginal delivery in 225 (83.0%) and CS in 46 (17.0%) cases. The intra-class correlation coefficient between manual and automated psAOP was 0.866, but automated psAOP was 4.6° wider than manual measurement. All TPU parameters had an inter-observer intra-class correlation coefficient > 0.800. Significant independent prediction of CS and CS-NP was provided by maternal factors, previous vaginal delivery, and psAOP. There was no improvement in area under the receiver-operating characteristic curve with the addition of psAOP to maternal factors. Conclusions: All TPU parameters are reproducible. Comparing the three TPU parameters for fetal head station, only psAOP is a significant independent predictor of CS; however, it is unlikely to be useful in predicting IOL outcome.

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This novel transverse approach for the measurement of UtA-PI in the first trimester appears to be comparable with the sagittal approach in terms of reliability, reproducibility and time required, and may be easier to perform. Providing accelerated onsite training can be helpful for improving the reliability of UtA-PI measurements and could potentially facilitate the broad implementation of first-trimester pre-eclampsia screening. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.